Patent GB-1098133-A (GB)
Title: Improvements relating to radar apparatus
Inventor: VOLES ROGER
IPC: G01S13/64
Filed: 1964-02-27
Abstract: 1,098,133. Pulse radar. ELECTRIC & MUSICAL INDUSTRIES Ltd. March 1, 1965 [Feb. 27, 1964], No. 8298/64. Heading H4D. The object of the invention is to produce a rectangular co-ordinate range/speed display of all targets in a particular direction. The pulse repetition frequency F, beam width and beam rotation speed are such that any one target produces N echoes. This allows the unambiguous possible Doppler frequency variations   of O c/s. to F/2 c/s. to be analysed with a resolu-   tion of F/N c/s., giving N/2 Doppler cells. The pulse echoes are coherently detected at 9 so that a moving target of range R will produce a variation in the amplitude of corresponding parts of successive outputs of detector 9 having a Doppler frequency fDR. If this variation is Fourier analysed, then, if the amplitude of the detector output for the rth return is Rr, then for all the returns, the component of the variation having a frequency nF/N (i.e., the nth Doppler cell), can be split into two quadrature components :- nF Thus if fDR=-, then Rr is synchronous with N 2# 2# Cos (- nr) and Sin (- nr) such that a n  and b n  N N become the sums of squared (always positive) sinusoidal functions and sum to large signals. nF If, however, #DR = - then a n  and b n  both N sum to zero. Each return is displayed as a vertical range trace A on long persistence CRT 10. Since the brightness of this trace is to represent Rr which can have negative as well as positive values, either the brightness must be biased around some brightness represent Rr=0, or the positive parts of the trace must be displayed first, followed by the negative parts. Either components a n  or b n  may be synthesised to separate out the Doppler cells, or both can be synthesised, then squared and added-but this is not necessary. The synthesis of component an only will thus be considered. The trace of tube 10 is scanned horizontally across the screen of an image intensifier tube 12. Synchronously with this scanning the trace is amplitude (intensity) modulated according to Cos (2#/N nr) (n being   the variable) by means of a Kerr cell 14 suitably controlled by function generator 15. Alternatively, the generator 15 can control the voltage of the first stage of intensifier 12. To allow for negative values of Cos (2#/N nr) each range/ Doppler cell on the output screen of intensifier 12 can be divided into upper positive and a lower negative halves, the correct result being obtained by making the negative parts of 2# Cos (- nr) positive and by algebraic subtrac- N tion of the brightness of the two halves. Negative values of the weighting function may be avoided by making it [1+Cos (2#/N nr)]. The final images on the output screen is the contribution of RrCos (2#/N nr) for one value of r and all values of R, to an for all values of R (ranges), i.e., the desired final display B. Thus the successive N returns produce successive contributions which are integrated on the output screen of intensifier 12 to produce display B. This may be viewed by camera tube 17 and the resulting signal used for P.P.I &c. processing.